What is the colour of the franciscana (Pontoporia blainvillei)? a review and a proposed assessment method

M. Trimble, R. Praderi

Abstract

Colouration pattern is suggested as a potentially useful characteristic to identify populations of franciscana (Pontoporia blainvillei). Such information is needed for the creation of management and conservation plans for the species. The existence of geographic variation in the colour of the franciscana has been hypothesized; it is suggested that Brazilian and Uruguayan individuals are greyish, while the Argentinean are brownish. We examined individuals from Uruguay using an objective method (Villalobos and Villalobos, 1947) to determine colour patterns. We also reviewed the variation of the colour pattern of the franciscana throughout this species' distribution as noted in the published literature. In the original description of the species in 1844 and in several subsequent papers during the 19th century, the colour pattern of the franciscana was erroneously described (e.g. as black and white). Only since the 20th century have the colouration descriptions approximately matched the actual specimens observed. These descriptions can be typically divided into two basic classes: greyish and ochre/brown. However, within these two general colour groups there is great variation. Several descriptions provided by Brazilian, Uruguayan, and Argentinean authors agree with the above hypothesis. The great variation within the modern descriptions of the franciscana's colour suggests that a variety of factors must be involved; therefore, we conclude that on the basis of the literature alone, it is very difficult to decide whether differences really exist in the franciscana's colour along its distribution. According to Villalobos and Villalobos (1947), the colour pattern of Uruguayan specimens could be interpreted as 'greyish dorsally and yellowish-grey laterally'. Due to some limitations found in this technique, we propose a new method based on the RGB ('red, green, blue') system that may fulfill our expectations for an objective procedure to determine colouration patterns. This standardized method would allow for a reliable comparison of colour patterns among franciscana populations.